docs: def calibrate_percentile_ranks(allele, predictor, peptides=None):
      """
      Private helper function.
      """
      global GLOBAL_DATA
      if peptides is None:
          peptides = GLOBAL_DATA["calibration_peptides"]
      predictor.calibrate_percentile_ranks(
          peptides=peptides,
          alleles=[allele])
      return {
          allele: predictor.allele_to_percent_rank_transform[allele],
      }